Advances in display technology have greatly enhanced the accessibility of digital information. The size of projector systems, for example, has significantly decreased, making them valuable accessories to even mobile devices, e.g., mobile communication devices. In this regard, a user of a mobile device can project a digital image from the device onto almost any surface, like a nearby wall, the palm of his or her hand, or any substantially opaque surface suitable as a projection surface. Projection conveniently magnifies the image for viewing, as compared to viewing the image on the device itself.
As another example, heads-up displays (HUDs) are becoming more prominent display accessories for military and commercial aviation, automobiles, gaming, and the like. HUDs display a digital image on a transparent screen placed in front of a user. From the perspective of the user, then, HUDs superimpose the digital image onto the surface(s) behind the screen. This allows the user to more quickly, more easily, and more safely view the image without looking away from his or her desired viewpoint. For instance, with such technology a driver of an automobile can view navigational instructions or speed information without taking his or her eyes off the road, a fighter pilot can view target information or weapon status information without taking his or her eyes off of the target, and so on. And although for perhaps less practical advantages than these, some computer laptops, mobile communication devices, and other such mobile devices are now equipped with transparent screens as well.
The fact that these display technologies make it possible to conveniently project or superimpose a digital image onto almost any surface is of course one of their advantages. However, that fact also creates a practical challenge. Because a digital image can be projected or superimposed onto almost any surface, all or parts of the digital image may sometimes be difficult for a user to perceive. Consider, for example, a digital image that includes green text. If the surface onto which the digital image is projected or superimposed is a green surface (e.g., a green wall or a patch of green trees), the green text will be much more difficult for the user to perceive than if the surface had instead been a purple surface (e.g., a purple wall or a patch of purple flowers).
Of course in many cases a user cannot practically change the surface(s) onto which he or she projects or superimposes a digital image, to achieve better perceptibility. In the case of an automobile heads-up display, for instance, such would require changing the direction of the entire automobile. Moreover, even in those cases where it may indeed be practical, surface(s) that offer better perceptibility may nevertheless be unavailable.